the most common cause of hypothyroidism
is Hashimoto :

An Autoimmune destruction of the thyroid gland :

caused by a viral infection

Pain in the neck

It has Oxyphil cells:

Follicular atrophy can be seen in Subacute  Lymphocytic thyroiditis

abnormalities of thyroid function is presented with palpation thyroiditis :

Known as"silent" or "painless" thyroiditis

The Histologic features of subacute lymphocytic Thyroiditis is similar to Hashimoto's Thyroiditis except the presence of follicular atrophy and Hurthle cell metaphasia

It is usually an incidental finding in
specimens resected

Hashimoto's Thyroiditis presents with painful enlargement thyroid

The most common cause of hyperthyroiditis in areas of the world where iodine levels are sufficient